The present invention relates to a system for measuring the distance and the relative speed between objects.
Such a system may be used, for example, in connection with adaptive driving speed control. In such a case, the system is used for measuring the distance and the relative speed between vehicles. On the basis of certain distance and relative speed values, the system for adaptive driving speed control influences the driving speed of the motor vehicle. A system of this type may be referred to as Adaptive Cruise Control (ACC).
The German Published Patent Application No. 42 42 700 discusses a method for measuring the distance and speed of objects with the aid of electromagnetic waves. The frequency of an emitted signal is modulated. The signals received during the increase and decrease of the emitted signal""s frequency are mixed with the emitted signal. The intermediate frequency signals created by that mixing are spectrally analyzed. The distance and the speed of at least one object are calculated from the frequency of the intermediate frequency signal""s spectral lines during at least one increase and at least one decrease of the frequency of the emitted signal.
A radar instrument having reduced beam power is referred to in German Patent No. 195 29 173. As characterized, the power radiated by a radar unit, on the average, is controlled as a function of the speed of the vehicle in which the radar unit is installed. At the same time, the time range during which a radar unit transmits radar signals is set proportional to the speed, and the transmission angle at which radar signals are radiated are also controlled as a function of the speed, and the aim of this radar unit is apparently to reduce the average beam power radiated from the radar unit, without impairing the measuring sensitivity. As further characterized, a further development of the radar unit is apparently based on enlarging the time gaps between the time ranges in which power is beamed with decreasing speed of the vehicle. Furthermore, the possibility is discussed of not radiating any radar signals below a predefined speed, above all from a standing vehicle, since no data may be needed in this speed range for an adaptive vehicle speed regulation. It is further discussed how to reduce the radiating load additionally by diminishing the angular range in which the radar is radiated with increasing speed of the vehicle.
The German Patent No. 195 29 173 also apparently discusses the possibility of unsymmetrically aligning the angular ranges of the radar rays with reference to the travel direction of the vehicle. For change in the time range, German Patent No. 195 29 173 apparently starts from the idea that, at low speeds (speed  less than 60 km/h), which may occur predominantly in city traffic, a shorter range of the radar unit is sufficient and no arbitrarily large relative speeds occur, so that the modulation rate at constant modulation amplitude can be selected greater than for greater speeds (speeds  greater than 60 km/h), which may occur primarily on superhighways and country roads. Modulation rate is defined as the quotient of modulation amplitude and modulation duration. By changing the modulation duration, the maximum range of the radar unit for low speeds is set at 70 m. Since modulation amplitude apparently remains constant in German Patent No. 195 29 173, at a greater modulation rate, the modulation amplitude is passed through in a shorter time. As characterized, it follows from this, that, at a shorter range, the modulation duration may be selected correspondingly shorter. The lower the vehicle speed, the shorter the range of the radar unit that is selected by the computer, and the shorter the modulation duration at fixed modulation amplitude, and the shorter the transmission time for the transmitter for sending one modulation amplitude. As a consequence, the time for receiving a modulation amplitude becomes shorter too. And then, the duration of the receiving condition of the radar unit also becomes shorter with decreasing speed of the vehicle.
In German Patent No. 195 29 180 is apparently discussed a circuit arrangement having a radar unit for ascertaining a distance or a relative speed. As characterized, the radar unit continually sends frequency modulated radar signals with variously large modulations rates, as a function of the speed of the vehicle in which the radar unit is mounted. The German Patent No. 195 29 180 discusses the modulation rate as the change of frequency per time unit. A larger modulation rate at constant maximum frequency yields a better distance resolution, which is an advantage especially in the low speed range. As indicated, the aim of the circuit arrangement is apparently to adapt to different speeds of the vehicle. By adapting the modulation rate of the radar unit to the speed of the vehicle, the range and accuracy of the radar unit are adjusted to the speed of the vehicle, and this may put at one""s disposal more accurate information on the distance and the relative speed. As characterized, according to one specific embodiment of German Patent No. 195 29 180, the radar unit consecutively and alternatingly uses a modulation cycle having a large modulation rate and a modulation cycle having a small modulation rate. This purportedly yields an accurate distance value for the near range as well as an accurate distance value for the distant range. At an increase of the modulation rate by a factor of 2, using the circuit arrangement, this purportedly leads to a halving of the range in which the distance from the object can be determined. On the other hand, the resolution of the distance is increased. The resolution of the speed remains constant. Also as characterized, with respect to a further specific embodiment of the circuit arrangement, in place of switching between a small and a large modulation rate, the modulation rate is continually adapted to the speed of the vehicle in such a way, that the modulation rate is increased with decreasing speed. Purportedly, in doing this, the modulation rate is interpolated appropriately to the speed of the vehicle, depending on the predefined speeds and the corresponding modulation rate. Depending on the driving dynamics points of view, the interpolation is carried out, for instance, linearly or hyperbolically. In the xe2x80x9cnormalxe2x80x9d case, the interpolation is apparently linear.
An exemplary embodiment and/or method of the present invention may provide a system and/or method for measuring the distance and relative speed between objects, which can be adapted to varying driving situations as flexibly as possible.
An exemplary embodiment may include a system for measuring the distance and the relative speed between objects using electromagnetic waves, having an apparatus, arrangement or structure for sending electromagnetic waves from a first object and having an apparatus, arrangement or structure for receiving reflected electromagnetic waves from at least one second object, the frequency of the emitted signal being modulated in such a way, that the modulation frequency, during a first time segment, increases approximately linearly from a first to a second modulation frequency value, that the modulation frequency, during a second time segment, is approximately constant, that the modulation frequency, during a third time segment, decreases approximately linearly from the second to a third modulation frequency value, that the modulation frequency, during a fourth time segment, is approximately constant, and that these time segments recur repeatedly, at least one of the modulation frequency values and/or the duration of at least one time segment changeable. It is believed that changing at least one of the modulation frequency values and/or the duration of at least one time segment may provide a maximum possible flexibility of the system.
With respect to another exemplary embodiment, it is believed to be advantageous if the change is dependent on at least the measured distance and/or the measured relative speed between the first object and the second object. On account of this dependence, the quantities distance and relative speed, which may be important in a system for measuring the distance and the relative speed between objects by of electromagnetic waves, are taken into consideration during the change of the at least one modulation frequency value and/or the duration of at least one time segment.
It is believed to be advantageous here, if the change of the modulation frequency value and/or of the time segment are functions, linearly, logarithmically or according to stored value pairs, of the measured distance and/or of the measured relative speed. It is believed that this solution may offer the advantage that the system can be adapted so that the user of the system gets an adaptive adjustment which the user would have selected in the same or similar manner if he had undertaken the change manually.
It is also believed to be advantageous if the modulation frequency values and/or the duration of the time segments are constant for predetermined value ranges of measured distance and/or relative speed, and if, when exceeding the predetermined value ranges, the modulation frequency values and/or the duration of the time segments is/are changed manually. Here, it is also believed to be advantageous when the appropriate steps can also be manually selected.
Furthermore, it is also believed to be advantageous when, the smaller the measured distance is, the larger the difference is selected to be between the second and the first modulation frequency value, and/or the larger the difference is selected to be between the second and the third modulation frequency value, and vice versa. This may provide an optimal adaptation to the boundary conditions to be expected when using the system.
It is also believed to be advantageous when the smaller the measured distance is and/or the larger the absolute value of the relative speed is, the smaller the first time segment and the third time segment are selected to be, and vice versa.
It is, again, also believed to be advantageous if the first and the third modulation frequency value are identical or essentially identical, and the modulation frequency has a trapeze-shaped pattern. In what is believed to be another comparably advantageous manner, it is possible that the first and the third time segment, and the second and the fourth time segment, respectively, have the same duration. Additionally, it is also believed to be advantageous if the duration of the second and the fourth time segment tends to 0, and the modulation frequency has a sawtooth-shaped pattern.
In what is believed to be another advantageous manner, the system is used in a motor vehicle. In this application, in turn, it is believed to be advantageous if the change of the frequency values and/or of the duration of the time segments is dependent on the driving situation. It is believed that this solution may offer the advantage that the change of the modulation frequency values and/or the duration of the time segments is undertaken so as to give the driver of the motor vehicle the feeling of optimal control response.
A variation of the system that is also believed to be advantageous involves the condition when the modulation frequency or the duration of the time segments are constant.
It is believed that one advantageous refinement provides that the modulation frequency values be changed to optimize the distance measurement, and that time segments be changed to optimize the relative speed measurement.